Systems, devices and methods related to reactive evaporation of refractory materials

ABSTRACT

Systems, devices and methods related to reactive evaporation of refractory materials. In some embodiments, a method for performing reactive evaporation can include positioning a volume of refractory material such as tantalum within an evaporation chamber and forming a vacuum environment therein. The method can further include providing a beam of electrons to the volume of refractory material to evaporate the refractory material into evaporated particles. The method can further include introducing a flow of reactive gas such as nitrogen into the evaporation chamber to allow at least some of the reactive gas to react with at least some of the evaporated particles of the refractory material. The flow of reactive gas can be selected such that a layer such as tantalum nitride formed on a substrate by deposition of the evaporated particles includes a range of a desirable property.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to U.S. Provisional Application Nos.61/897,802 filed Oct. 30, 2013, entitled SYSTEMS, DEVICES AND METHODSRELATED TO REACTIVE EVAPORATION OF REFRACTORY MATERIALS, and 61/897,814filed Oct. 30, 2013, entitled REFRACTORY METAL BARRIER IN SEMICONDUCTORDEVICES, the disclosure of each of which is hereby expresslyincorporated by reference herein in its entirety.

BACKGROUND

1. Field

The present disclosure generally relates to reactive evaporation ofrefractory materials.

2. Description of the Related Art

In some semiconductor fabrication processes, formation of a layer on asubstrate such as a wafer can be achieved by an evaporation process. Insituations where thermal evaporation may not be suitable, techniquessuch as electron-beam (also referred to as e-beam) evaporation can beutilized.

Electron-beam evaporation is a deposition process where source materialis heated by a beam of electrons to yield evaporated atoms or particlesthat are deposited on exposed surfaces. E-beam evaporation can bepreferable over thermal evaporation when, for example, higher densitydepositions are desired. Further, under ideal operating conditions,electron-beam only heats the source material and not the holder such asa crucible or a hearth. Since the holder is not heated as in thermalevaporation, contamination from the holder is typically lowered.

SUMMARY

According to some implementations, the present disclosure relates to amethod for performing reactive evaporation. The method includespositioning a volume of refractory material to be evaporated within anevaporation chamber, and forming a vacuum environment within theevaporation chamber. The method further includes providing a beam ofelectrons to the volume of refractory material to evaporate therefractory material into evaporated particles. The method furtherincludes introducing a flow of reactive gas into the evaporation chamberto allow at least some of the reactive gas to react with at least someof the evaporated particles of the refractory material. The flow ofreactive gas is selected such that a layer formed on a substrate bydeposition of the evaporated particles includes a range of a desirableproperty.

In some embodiments, the refractory material can include tantalum (Ta),and the reactive gas can include nitrogen gas (N2). The layer caninclude tantalum nitride (TaN). The tantalum nitride can have acomposition expressed as TaN_(x), with the quantity x having a value ina range between 0 and 0.5.

In some embodiments, the desirable property can include a mechanicalproperty. The selected flow of reactive gas can be in a range having alower flow limit and an upper flow limit. The lower flow limit of therange can be selected to correspond to be at or higher than a first flowrate that yields a first stress level associated with the layer. Thefirst stress level can include a stress level associated with transitionbetween tensile stress and compressive stress associated with the layer.The first stress level can have a value of approximately zero.

In some embodiments, the lower flow limit of the range can be selectedsuch that the layer provides a compressive stress to the substrate. Thelower limit and the upper limit of the range can be selected such thatthe compressive stress has a magnitude less than a selected value. Thelower limit of the range can be selected such that the compressivestress varies sufficiently slowly as a function of the flow to besubstantially reproducible.

In some embodiments, the desirable property can include an electricalproperty. The electrical property can include a sheet resistanceassociated with the layer. The sheet resistance can increase as afunction of the flow of the reactive gas. The upper limit of the rangecan be selected such that the sheet resistance associated with the layeris less than a selected sheet resistance value.

In some embodiments, the method can further include forming one or moreadditional layers over the layer formed with the flow of reactive gas.Each of the one or more additional layers can be formed by electron-beamevaporation, such that all of the layers can be formed utilizing onephotolithography and one deposition type.

In some implementations, the present disclosure relates to a reactiveevaporation system that includes an evaporation chamber configured tohold a volume of refractory material to be evaporated. The systemfurther includes a vacuum system in communication with the evaporationchamber, with the vacuum system being configured to provide a vacuumenvironment within the evaporation chamber. The system further includesan electron-beam system configured to provide a beam of electrons to thevolume of refractory material to evaporate the refractory material intoevaporated particles. The system further includes a gas supply system incommunication with the evaporation chamber. The gas supply system isconfigured to provide a flow of reactive gas into the evaporationchamber to allow at least some of the reactive gas to react with atleast some of the evaporated particles of the refractory material. Theflow of reactive gas is selected such that a layer formed on a substrateby deposition of the evaporated particles includes a range of adesirable property.

According to some implementations, the present disclosure relates to amethod for forming a metalized stack on a semiconductor substrate. Themethod includes mounting the semiconductor substrate within anevaporation chamber, and positioning a volume of refractory material tobe evaporated within the evaporation chamber. The method furtherincludes forming a vacuum environment within the evaporation chamber.The method further includes depositing a refractory material barrierlayer on the semiconductor substrate. The depositing includes providinga beam of electrons to the volume of refractory material to evaporatethe refractory material into evaporated particles. The depositingfurther includes introducing a flow of reactive gas into the evaporationchamber to allow at least some of the reactive gas to react with atleast some of the evaporated particles of the refractory material. Theflow of reactive gas is selected such that the refractory materialbarrier layer includes a range of a desirable property.

In some embodiments, the method can further include forming one or moreadditional layers over the refractory material barrier layer. The one ormore additional layers can include a second layer formed over therefractory material barrier layer. The second layer can be configured asa diffusion barrier, an adhesion layer, or a layer having a desiredelectrical property. The second layer can include a titanium (Ti) layer.

In some embodiments, the one or more additional layers can furtherinclude a conductive metal layer formed over the second layer. Theconductive metal layer can include a gold (Au) layer.

In some embodiments, the one or more additional layers can furtherinclude a passivation layer formed over the conductive metal layer. Thepassivation layer can include a titanium (Ti) layer. In someembodiments, each of the refractory material barrier layer, the adhesionlayer, the conductive metal layer, and the passivation layer can beformed by electron-beam evaporation utilizing one photolithography andone deposition type.

In some embodiments, the metalized stack can include a gate structure ofa transistor. The transistor can include a pseudomorphic high electronmobility transistor (pHEMT).

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an electron-beam (e-beam) evaporator thatcan be utilized to implement one or more features as described herein.

FIG. 2 shows a more specific example of the evaporator of FIG. 1.

FIG. 3 shows a more specific example of the evaporator of FIG. 2.

FIG. 4 shows a process that can be implemented to form a layer ofrefractory material having one or more desirable properties on asubstrate such as a semiconductor wafer.

FIG. 5 shows an example of how mechanical stress associated with a layerof deposited refractory material can change as a function of flow rateof a reactive gas such as nitrogen.

FIG. 6 shows an example of how sheet resistance associated with a layerof deposited refractory material can change as a function of flow rateof a reactive gas such as nitrogen.

FIG. 7 shows a more generalized example of how flow rate orconcentration of reactive gas can be selected to yield desirablemechanical and/or electrical properties associated with a depositedlayer.

FIG. 8 shows a more generalized example of how an operating conditioncan be selected to yield desirable first and/or second propertiesassociated with a deposited layer.

FIG. 9 shows an example focused ion beam (FIB) image of a metal stackthat includes a refractory material layer formed utilizing a techniquehaving one or more features as described herein.

FIG. 10 schematically depicts a stack configuration that can beimplemented utilizing one or more features of the present disclosure togenerate a metal stack such as the example of FIG. 9.

FIG. 11 shows an example of the sheet resistance performance can bemaintained over different fabrication runs.

FIG. 12 shows an example of standard deviation for the example sheetresistance performance being maintained of the different fabricationruns.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

In some semiconductor fabrication processes, formation of arefractory-material layer on a substrate such as a wafer can bedesirable. Examples of such a refractory-material layer are describedherein in greater detail.

In some implementations, such a layer can be formed by an evaporationprocess; and in situations where thermal evaporation may not besuitable, techniques such as electron-beam (also referred to as e-beam)evaporation can be utilized. Electron-beam evaporation is a depositionprocess where source material is heated by a beam of electrons to yieldevaporated atoms or particles that are deposited on exposed surfaces.E-beam evaporation can be preferable over thermal evaporation when, forexample, higher density depositions are desired, which can be achievedby a relatively large amount of energy delivered to the source materialby electrons. Further, under ideal operating conditions, electron-beamonly heats the source material and not the holder such as a crucible ora hearth. Since the holder is not heated as in thermal evaporation,contamination from the holder is typically lowered.

In some situations, refractory materials can fragment during e-beamevaporation, thereby resulting in changes in properties. Such materialscan be deposited on the substrate by, for example, reactive evaporation,where reactive gas can be introduced to evaporants resulting from e-beamheating of the source material. Under selected conditions, suchevaporants can react with the reactive gas to form a layer on thesubstrate, and such a layer can have desirable properties. Non-limitingexamples of such reactive gas and desirable properties are describedherein in greater detail.

FIG. 1 schematically depicts an e-beam evaporator 100 that can beutilized to implement evaporation techniques having one or more featuresas described herein. The e-beam evaporator 100 is depicted as having avolume of source material 106 held in a holder such as a crucible 108(also referred to herein as a hearth). A beam of electrons 104 is shownto be directed to a surface (e.g., upper surface) of the source materialso as to yield source particles 112 evaporating from a heated region110. Such source particles 112 (also referred to herein as evaporants)can be directed to any available directions from the heated region 110;and can travel in a line-of-sight manner. Thus, in the example of FIG.1, parts (e.g., semiconductor wafers) 114 a-114 c on which a film of thesource material is to be formed can be positioned appropriately toreceive such source particles 112.

Because of the foregoing nature of the evaporants, an emitter 102 ofelectron-beam is typically positioned so that evaporants generally donot reach and undesirably coat the emitter 102. For example, the emitter102 is shown to be positioned below the source material holder 108 so asto be out of the line-of-sight travel of the evaporants 112.

To deliver the electron-beam 104 from the emitter 102 to the uppersurface of the source material 106, magnetic field (B, depicted as anarrow 116) can be provided to bend the trajectories of the electrons. Inthe example of FIG. 1, a constant static magnetic field is depicted asgoing into the plane of illustration. Accordingly, an electrontravelling within the plane with a speed of v experiences a magneticforce with a magnitude of evB and a direction that is perpendicular tothe direction of travel. The resulting motion of the electron generallydefines, for example, about 270 degrees of a circular path, therebyallowing electrons from the “hidden” emitter 102 to be delivered to theupper surface of the source materials 106 in a curved manner.

FIG. 1 further shows that in some embodiments, the e-beam evaporator 100can include or be in communication with a vacuum component 124configured to provide a desirable vacuum or reduced pressure within theevaporator 100. Examples of such a vacuum component are described hereinin greater detail.

FIG. 1 further shows that in some embodiments, the e-beam evaporator 100can include or be in communication with a gas supply 122 configured toprovide a desirable flow of reactive gas into the evaporator 100.Examples of such a gas supply are described herein in greater detail.

FIG. 1 further shows that in some embodiments, the e-beam evaporator 100can include or be in communication with a controller 120 configured tocontrol or facilitate control of one or more features associated withthe operation of the evaporator 100. Examples of such control featuresare described herein in greater detail.

FIG. 2 shows an example evaporator 100 that can be a more specificexample of the evaporator of FIG. 1. In some embodiments, such anevaporator can be configured to implement reactive evaporation havingone or more features as described herein. In the example evaporator 100of FIG. 2, delivery of an electron-beam 104 from an emitter 102 to avolume of source material 106 being held by a holder 108 can beimplemented as described herein. Incidence of electrons on the sourcematerial 106 results in a heated region, from which evaporants 112 areemitted. Such evaporants are depicted as travelling in their respectivelines of sight to thereby be deposited on exposed surfaces of substratessuch as semiconductor wafers 134. As described herein, some or all ofsuch evaporants can react with reactive gas to yield one or more desiredproperties for the deposited layer on the wafers 134.

In the example evaporator 100 shown in FIG. 2, the wafers 134 can beheld in desired locations and orientations in a wafer-holder 132 toreceive the reacted evaporants 112. In the example shown, thewafer-holder 132 can be configured to rotate by a rotating mechanism 136that couples the wafer-holder 132 to a dome assembly 138. Such arotation of the wafer-holder 132 can yield a more uniform deposition ofevaporants among the various wafers 134.

In the example shown in FIG. 2, the dome assembly 138, a side wall 140,and a floor 144 can form a chamber 130 that includes an internal volume142. Such a volume can be provided with an appropriate level of vacuumor reduced pressure to facilitate the evaporation process. Such a vacuumor reduced pressure can be provided and/or facilitated by a vacuumcomponent 124 that is in communication with the chamber 130.

In the example shown in FIG. 2, reactive gas can be introduced into thechamber 130 by a gas supply component 122 to facilitate one or morefeatures of the reactive evaporation process as described herein.Examples of such a reactive gas and how the gas can be provided to thechamber 130 are described herein in greater detail.

As described herein, some or all of the foregoing techniques forperforming reactive evaporation can be controlled and/or facilitated bya controller 120. In some embodiments, such a controller can include aprocessor and a memory for storing, for example, data, executableinstructions, etc. Such a memory can be a computer readable medium(CRM), including a non-transitory CRM.

In some embodiments, some or all portions of the controller 120 can belocated with the evaporator 100, remotely located from the evaporator100, or any combination thereof. It will be understood that componentsof the controller 120 itself may be located generally together, incommunication from remote locations, or any combination thereof.

FIG. 3 shows and example reactive evaporation configuration 100 that canbe a more specific example of the evaporator 100 of FIG. 2. In FIG. 3,source material 106 can include tantalum (Ta) held by a hearth 108, andreactive gas can include nitrogen gas (N₂). Evaporation of tantalum byelectrons from an electron emitter 102 can react with the nitrogen gaswithin an evacuated volume 142 of a chamber 130 so as to allow formationof a tantalum nitride (TaN) layer on each of a plurality of wafers 134being held by a rotatable dome 132. Although described in the context oftantalum as a refractory material and nitrogen as a reactive gas, itwill be understood that other refractory materials and/or reactive gasescan also be utilized.

In the example of FIG. 3, the reactive evaporation configuration 100 caninclude a shutter 180 and a monitor such as a crystal monitor 150 tofacilitate automated monitoring and/or control (e.g., by a controlsystem 120) of thickness of a deposited layer on each of the wafers 134held by the rotating dome 132. Examples of how such crystal monitor 150and shutter 180 can be implemented, as well as additional detailsconcerning the rotatable wafer-holding dome 132, are described in U.S.Pat. No. 8,022,448 titled “APPARATUS AND METHODS FOR EVAPORATIONINCLUDING TEST WAFER HOLDER,” which is expressly incorporated byreference in its entirely.

In the example of FIG. 3, a desired vacuum or reduced pressure for thevolume 142 of the chamber 130 can be provided or facilitated by a vacuuminterface assembly 170. Such an assembly can be configured to provide,for example, a vacuum formation path (e.g., arrow 172) between thevolume 142 and a vacuum pump (not shown). In some embodiments, the levelof vacuum can be monitored by the control system 120 utilizing, forexample, a pressure gauge 174 that measures the pressure associated withthe evacuated volume 142. The control system 120 can be configured to,for example, operate the vacuum interface assembly 170 and/or the vacuumpump so as to decrease, increase, or maintain the pressure associatedwith the evacuated volume 142.

In the example of FIG. 3, a desired flow rate of the nitrogen gas can beprovided to the volume 142 of the chamber by, for example, a mass flowcontroller (MFC) 164. The MFC 164 is shown to be implemented along a gaspath 162 between a source (not shown) and a gas inlet 160. The gas inlet160 can be positioned within the volume 142.

In some embodiments, the level of flow rate of nitrogen gas introducedinto the evacuated volume can be monitored and/or controlled by thecontrol system 120 utilizing, for example, the MFC 164. The controlsystem 120 can be configured to, for example, allow flow, stop flow,increase flow rate, decrease flow rate, time the duration of flow, etc.Such a control functionality can be utilized to obtain deposited TaNlayers having one or more desirable properties as described herein.

FIG. 4 shows a process 200 that can be implemented to performevaporation to yield a deposition layer having one or more advantageousfeatures as described herein. In block 202, one or more substrates suchas semiconductor wafers can be positioned in a chamber to form a layerof refractory material by evaporation deposition. In block 204, vacuumor reduced pressure can be provided in the chamber to facilitate theevaporation deposition. In block 206, reactive gas can be provided tothe chamber at a selected flow rate. In block 208, refractory materialcan be evaporated from a source with energetic electrons. In block 210,evaporation of the refractory material can be performed for a selectedduration to form a desired layer that includes the refractory materialon the substrate.

FIGS. 5 and 6 show examples of properties of layers that can result fromthe foregoing reactive evaporation process. FIG. 5 shows an examplewhere measured stress values resulting from 250 angstrom (A) thick TaNfilms are plotted for different nitrogen gas flow rates in standardcubic centimeters per minute (sccm). FIG. 6 shows an example wheremeasured sheet resistance values resulting from the 250 angstrom thickTaN films are plotted for the different nitrogen gas flow rates. Table 1lists the values of the data points plotted in FIGS. 5 and 6.

TABLE 1 Film N2 Sheet Deposition thickness flow rate Stress resistancerate (Å) (sccm) (MPa) Rs (Ω/sq) Sigma (Å/s) 250 0 767.8 81.13 1.886 0.5250 5 601.8 140.38 2.623 0.5 250 5 578.6 147.94 2.68 0.5 250 10 158.2139.26 2.622 0.5 250 12 455.5 96.212 2.139 0.5 250 15 −87.1 157.78 2.6440.5 250 15 −176.3 146.75 2.858 0.5 250 20 −182.4 176.16 3.261 0.5 250 60−111.2 364.89 4.426 0.5 250 100 −526.9 960 1.356 1

In the example shown in FIG. 5, stress data points having positivevalues can be considered to be tensile stresses on the substrateprovided by the respective deposited films (e.g., 250 Å thick filmshaving TaN). Stress data points having negative values can be consideredto be compressive stresses on the substrate provided by the respectivedeposited films (e.g., 250 Å thick films having TaN). One can see thatfor flow rates of N₂ between 0 and about 14 sccm, tensile stress resultsfrom the example 250 Å thick TaN film. At about 14 sccm and highervalues of N₂ flow rate, compressive stress results from the example 250Å thick TaN film.

In the example stress curve in FIG. 5, suppose that it is desirable toobtain a deposited TaN layer having a selected thickness (e.g., 250 Å)that results in a stress magnitude being less than some selectedthreshold value (e.g., about 200 MPa). Within the tensile stress regionresulting from relatively low N₂ flow rate values, one can see that thestress magnitudes either exceed the threshold value or fluctuate toorapidly. One can also see that there is a relatively rapid change instress in a relatively small range of N₂ flow rate, as tensile stresstransitions to a zero-stress level and then to compressive stress.

In the compressive stress region, however, there is a relatively largerange of N₂ flow rate (e.g., about 14 to 70 sccm) where the stressmagnitude remains below the example 200 MPa threshold value. Further,the compressive stress level is shown to change relatively smoothlywithin such a flow rate range, as well as beyond the range. As shown inFIG. 5, the stress level between about 15 to 22 sccm is relatively flatat a value of about 180 MPa. As described herein, at least some portionof such a range of N₂ flow rate can also yield a desired electricalproperty such as sheet resistance.

FIG. 6 shows a plot of measured sheet resistance values resulting fromthe example 250 angstrom thick TaN films deposited using differentnitrogen gas flow rates. One can see that the sheet resistance Rs (inunits of Ω/sq) generally increases as the N₂ flow rate increases.

In the example sheet resistance curve in FIG. 6, suppose that it isdesirable to obtain a deposited TaN layer having a selected thickness(e.g., 250 Å) that results in a sheet resistance Rs being less than someselected threshold value (e.g., Rs value corresponding to N₂ flow rateof about 22 sccm). Such below-threshold sheet resistance can be obtainedby utilizing N₂ flow rate that is less than 22 sccm. When the foregoingN₂ flow rate range (e.g., about 22 sccm or lower) that yields adesirable electrical property such as sheet resistance is consideredalong with the example N₂ flow rate range (e.g., about 15 sccm orhigher) that yields a desirable mechanical property such as stresslevel, one can see that an example N₂ flow rate range of about 15 to 22sccm can yield desirable results for both properties.

In the example results described in reference to FIGS. 5 and 6, the N₂flow rate is measured by the mass flow controller (MFC) 164 described inreference to FIG. 3. For a particular evaporator device, such a flowrate can yield a corresponding concentration of nitrogen at a desiredlocation within the evaporator device. For a different evaporatordevice, however, the same flow rate can yield a different concentrationat a similar desired location within that evaporator device.Accordingly, it will be understood that various concepts described inreference to the examples of FIGS. 5 and 6 can be implemented in a moregeneralized manner.

For example, FIG. 7 shows a configuration 300 where a distribution 310of a mechanical property and a distribution 320 of an electricalproperty are plotted as functions of reactive gas flow rate orconcentration. Such a concentration can be, for example, a concentrationat a desired location within an evaporator chamber. Such a desiredlocation can be, for example, at or near where wafers are located. Atsuch a location, the reactive gas concentration can be substantiallyuniform and generally representative of the reactive gas concentrationwithin the evaporator chamber.

In the example of FIG. 7, the mechanical property (e.g., stress level)can have a desired value (e.g., zero stress level). Relative to such adesired value, a desired range 312 can be specified; and such a desiredrange can include a selected upper limit that has a value greater thanthe desired value by an amount ΔP1. Similarly, the desired range 312 caninclude a selected lower limit that has a value less than the desiredvalue by an amount ΔP2. The values of ΔP1 and ΔP2 may or may not be thesame. In some situations, the desired range 312 can also be defined byan upper limit alone, or by a lower limit alone.

In the example of FIG. 7, the electrical property (e.g., sheetresistance) can have a desired range 322 that includes, for example,values less than or equal to a selected limit. In some situations, thedesired range 322 can also be defined by a lower limit, or by upper andlower limits.

Based on the foregoing example desired range 312 for the mechanicalproperty, one can see that a range of values for the reactive gas flowrate or values for concentration of the reactive gas in the evaporatorchamber can be from a lower limit 314 (where the curve 310 is at theselected upper limit) to an upper limit 318 (where the curve 310 is atthe selected lower limit). In the context of the stress level exampledescribed in reference to FIG. 5, the stress level may change toorapidly near such a lower limit 314, or even near another lower limit316 (where the curve 310 is at the desired value). Accordingly, a lowerlimit 317 can be selected to yield a range where the mechanical propertydoes not vary rapidly. In the example shown in FIG. 7, such a lowerlimit yields a range of horizontal axis values between limits 317 and318.

Based on the foregoing example desired range 322 for the electricalproperty, one can see that a range of values for the reactive gas flowrate or values for concentration of the reactive gas in the evaporatorchamber can include values that are less than or equal to an upper limit324. Thus, when such a range of values (flow rate or concentration)based on the electrical property is combined with ranges of values (flowrate or concentration) based on the mechanical property, a range ofvalues (flow rate or concentration) can be obtained to satisfy both ofthe desired mechanical and electrical properties. Such a range of valuescan have a lower limit of 330, 332 or 334 corresponding to the lowerlimits 314, 316 or 317 associated with the mechanical property curve310, and an upper limit 334 corresponding to the upper limit 324associated with the electrical property curve 320.

The example of FIG. 7 is described in the context of obtaining a rangeassociated with a reactive gas to satisfy desired ranges of a mechanicalproperty and an electrical property. FIG. 8 shows a more generalizedconfiguration 350 where one or more features of the present disclosurecan be implemented in a reactive evaporation process to obtain one ormore ranges associated with an operating condition to satisfy desiredrange(s) associated with one or more properties associated with adeposited refractory-material layer such as a TaN layer.

In the example of FIG. 8, a first property (e.g., mechanical propertysuch as stress level) can have a desired range 362; and a first propertycurve 360 can be within such a desired range (362) at one or more rangesof the operating condition (e.g., flow rate or concentration).Similarly, a second property (e.g., electrical property such as sheetresistance) can have a desired range 372; and a second property curve370 can be within such a desired range (372) at one or more ranges ofthe operating condition.

For the first property, one or more ranges of the operating conditionthat satisfy the range 362 are depicted as ranges 364 a to 364 b, 364 cto 364 d, 364 e to 364 f, 364 g to 364 h, and 364 i to 364 j. For thesecond property, one or more ranges of the operating condition thatsatisfy the range 372 are depicted as a range 374 a to 374 b.Accordingly, one or more ranges of the operating condition that satisfyboth of the ranges 362 and 372 of the first and second properties aredepicted as 380 (384 a to 384 b) and 382 (384 c to 384 d).

FIG. 9 shows a focused ion beam (FIB) image of an example metal stackthat includes a refractory material layer formed utilizing a reactiveevaporation technique having one or more features as described herein.The example metal stack can include a TaN layer (e.g., 150 Å) formedover a substrate. In the example, the substrate is shown to include alayer of silicon nitride (SiN) (e.g., 1,500 Å) formed over asemiconductor material such as gallium arsenide (GaAs). It will beunderstood that one or more features of the present disclosure can alsobe implemented on other types of semiconductor materials.

The example metal stack in FIG. 9 can further include a titanium (Ti)layer (e.g., 700 Å) formed over the TaN layer. The titanium (Ti) layeris typically easier to form by evaporation. Thus, the TaN layerunderneath the Ti layer can be relatively thin and provide one or morefunctionalities as described herein; and the Ti layer can providefunctionalities such as diffusion barrier (e.g., when the metalstructure is being used as a FET gate), Schottky barrier (e.g., when themetal structure is being used as a Schottky diode anode), adhesion,and/or desired electrical properties. The example metal stack canfurther include a gold (Au) layer (e.g., 500 Å) formed over the Tilayer. It will be understood that the thickness values are approximate,and can vary depending on particular designs.

FIG. 10 shows that in some embodiments, the example stack of FIG. 9 canfurther include a second Ti layer (e.g., thickness d4) formed over theAu layer. As described in reference to FIG. 9, various layers can havetheir thicknesses adjusted for different designs. More particularly, theTaN layer is depicted as having a thickness of d1, the first Ti layer isdepicted as having a thickness of d2, the Au layer is depicted as havinga thickness of d3, and the second Ti layer is depicted as having athickness of d4.

In some embodiments, TaN layers formed utilizing one or more features asdescribed herein can include relative content of tantalum and nitrogenthat can be expressed as a formula TaN_(x), where the quantity x can bein a range of 0.0 to 0.5. It will be understood that other ratios canalso be utilized.

FIGS. 11 and 12 show example plots of sheet resistance values andrelative variation values resulting from formation of a gate layerstructure over different runs (e.g., over time and/or using differentevaporator units), demonstrating that relatively consistent performanceresults can be expected utilizing one or more features of the reactiveevaporation techniques described herein. To form the example gate layerstructure, a chamber pressure of approximately 1.3×10⁻⁶ mbar wasprovided. A N₂ flow rate of approximately 20 sccm was provided forapproximately 240 seconds during a ramp or soak portion, before theshutter (e.g., 180 in FIG. 3) was opened or any TaN was deposited on thewafers, to provide sufficient nitrogen stabilization and uniformitythroughout the chamber. A TaN layer was formed by continuing the N₂ flowrate of approximately 20 sccm and opening the shutter to yield a TaNdeposition rate of approximately 0.5 Å/s. At such a deposition rate,reactive evaporation for approximately 300 seconds yielded a TaN layerhaving a thickness of approximately 150 Å.

A Ti layer was formed over the TaN layer utilizing an electron-beamevaporation deposition process. A deposition rate of approximately 2.0Å/s was utilized; and the overall thickness of the Ti layer wasapproximately 250 Å.

A Au layer was formed over the Ti layer utilizing an electron-beamevaporation deposition process. A deposition rate of approximately 10.0Å/s was utilized; and the overall thickness of the Au layer wasapproximately 4,500 Å.

Another Ti layer was formed over the Au layer utilizing an electron-beamevaporation deposition process. A deposition rate of approximately 1.010.0 Å/s was utilized; and the overall thickness of the Ti layer wasapproximately 30 Å.

Table 2 lists the average sheet resistance (Rs) values and the relativevariation (stdev) values for the six different gate layer fabricationruns plotted in FIGS. 11 and 12. The Rs values were measured for gatelayers on wafers without being patterned into gate structures. For suchmeasurements, an average of about 49 data points were measured across agiven wafer with about 5 mm edge exclusion. One can see that the averagesheet resistance (Rs) values associated with the six runs are fairlyconsistent and reproducible in a range of about 0.0625 to 0.0655 ofΩ/sq. One can also see that the standard deviation of the Rs valuesassociate with the six runs are also fairly consistent and reproduciblein a range of about 1.0 to 1.3%.

TABLE 2 Run Rs (Ω/sq) Stdev (%) 1 0.0640 1.157 2 0.0627 1.026 3 0.06251.004 4 0.0636 1.047 5 0.0646 1.157 6 0.0654 1.293

As described herein by way of examples, the formation of TaN layer canbe advantageously implemented by a reactive evaporation technique, wherereactive gas such as nitrogen can be provided through a gas supplysystem to a standard evaporation system. As also described herein,optimum or desired deposition conditions can be determined based onfinding, for example, a N₂ gas flow rate (or corresponding nitrogenpressure inside the chamber) in a range where a property such as filmstress level is at a desired range and also relatively insensitive tosmall changes in the flow rate. Under such deposition conditions, thecomposition of the film can be controlled easily, and the resulting filmcan provide excellent barrier properties. As also described herein,electrical resistance of such a film in the vertical direction can bevery low (e.g., due to low thickness).

From a fabrication perspective, the ability to form arefractory-material layer such as a TaN layer utilizing electronevaporation as described herein can allow implementation of a one-step(e.g., one photolithography and one deposition type) process forfabricating layered structures such as gate or interconnect structures.For example, and as described herein in reference to FIGS. 9-12, eachlayer of the example TaN—Ti—Au—Ti stack can be formed utilizing anelectron evaporation process utilizing each layer's respective sourcematerial. With the TaN layer, reactive gas can be provides as describedherein; and introduction and removal of such gas to and from theevacuated chamber can be implemented relatively easily without breakingvacuum of the chamber.

As described herein, sheet resistance of a TaN_(x) film can be adjustedby, for example, flow rate of a reactive gas such as nitrogen.Accordingly, a device having such a TaN_(x) film can be implemented as athin-film resistor (TFR).

In some embodiments, a TaN_(x) layer formed as described herein can beimplemented on, for example, III-V semiconductors such as galliumarsenide (GaAs) substrates. In the context of the TFR, evaporationmethod allows use of a lift-off technique to define the resistor,essentially eliminating various problems associated with dielectricassisted lift-off (DAL) technique typically utilized in sputterdeposition. In addition, the TaN resistor can be formed directly on, forexample, silicon nitride, so as to make the TFR less susceptible toleakage through the GaAs substrate.

Tantalum is a refractory metal with a very high melting point which isgenerally a challenge to evaporate. However, as described herein,systems, devices and method for depositing TaN_(x) layers with electronbeam evaporation with nitrogen incorporation can yield a stable TaN_(x)film having some of all desired properties of a sputtered TaN layer.

It is noted that in an evaporated TaN_(x) film, the amount of nitrogenincorporated into the film can be dependent not only on the N₂ flow, butalso on the level of background oxygen and carbon within the chamberand/or the source. Such an effect of oxygen in the film can be addressedor minimized by, for example, controlling the presence of oxygen (e.g.,by maintaining low level of oxygen in the film).

The foregoing example of the evaporated TaN TFR is one of a number ofdevices for which one or more features of the present disclosure can beutilized to fabricate such devices. Other non-limiting examples relatedto TaN layers can be found in U.S. patent application Ser. No. ______[Attorney Docket 75900-50059US], titled “REFRACTORY METAL BARRIER INSEMICONDUCTOR DEVICES,” filed on even date herewith, which is expresslyincorporated by reference in its entirely, and which is to be consideredpart of the specification of the present application.

The present disclosure describes various features, no single one ofwhich is solely responsible for the benefits described herein. It willbe understood that various features described herein may be combined,modified, or omitted, as would be apparent to one of ordinary skill.Other combinations and sub-combinations than those specificallydescribed herein will be apparent to one of ordinary skill, and areintended to form a part of this disclosure. Various methods aredescribed herein in connection with various flowchart steps and/orphases. It will be understood that in many cases, certain steps and/orphases may be combined together such that multiple steps and/or phasesshown in the flowcharts can be performed as a single step and/or phase.Also, certain steps and/or phases can be broken into additionalsub-components to be performed separately. In some instances, the orderof the steps and/or phases can be rearranged and certain steps and/orphases may be omitted entirely. Also, the methods described herein areto be understood to be open-ended, such that additional steps and/orphases to those shown and described herein can also be performed.

Some aspects of the systems and methods described herein canadvantageously be implemented using, for example, computer software,hardware, firmware, or any combination of computer software, hardware,and firmware. Computer software can comprise computer executable codestored in a computer readable medium (e.g., non-transitory computerreadable medium) that, when executed, performs the functions describedherein. In some embodiments, computer-executable code is executed by oneor more general purpose computer processors. A skilled artisan willappreciate, in light of this disclosure, that any feature or functionthat can be implemented using software to be executed on a generalpurpose computer can also be implemented using a different combinationof hardware, software, or firmware. For example, such a module can beimplemented completely in hardware using a combination of integratedcircuits. Alternatively or additionally, such a feature or function canbe implemented completely or partially using specialized computersdesigned to perform the particular functions described herein ratherthan by general purpose computers.

Multiple distributed computing devices can be substituted for any onecomputing device described herein. In such distributed embodiments, thefunctions of the one computing device are distributed (e.g., over anetwork) such that some functions are performed on each of thedistributed computing devices.

Some embodiments may be described with reference to equations,algorithms, and/or flowchart illustrations. These methods may beimplemented using computer program instructions executable on one ormore computers. These methods may also be implemented as computerprogram products either separately, or as a component of an apparatus orsystem. In this regard, each equation, algorithm, block, or step of aflowchart, and combinations thereof, may be implemented by hardware,firmware, and/or software including one or more computer programinstructions embodied in computer-readable program code logic. As willbe appreciated, any such computer program instructions may be loadedonto one or more computers, including without limitation a generalpurpose computer or special purpose computer, or other programmableprocessing apparatus to produce a machine, such that the computerprogram instructions which execute on the computer(s) or otherprogrammable processing device(s) implement the functions specified inthe equations, algorithms, and/or flowcharts. It will also be understoodthat each equation, algorithm, and/or block in flowchart illustrations,and combinations thereof, may be implemented by special purposehardware-based computer systems which perform the specified functions orsteps, or combinations of special purpose hardware and computer-readableprogram code logic means.

Furthermore, computer program instructions, such as embodied incomputer-readable program code logic, may also be stored in a computerreadable memory (e.g., a non-transitory computer readable medium) thatcan direct one or more computers or other programmable processingdevices to function in a particular manner, such that the instructionsstored in the computer-readable memory implement the function(s)specified in the block(s) of the flowchart(s). The computer programinstructions may also be loaded onto one or more computers or otherprogrammable computing devices to cause a series of operational steps tobe performed on the one or more computers or other programmablecomputing devices to produce a computer-implemented process such thatthe instructions which execute on the computer or other programmableprocessing apparatus provide steps for implementing the functionsspecified in the equation(s), algorithm(s), and/or block(s) of theflowchart(s).

Some or all of the methods and tasks described herein may be performedand fully automated by a computer system. The computer system may, insome cases, include multiple distinct computers or computing devices(e.g., physical servers, workstations, storage arrays, etc.) thatcommunicate and interoperate over a network to perform the describedfunctions. Each such computing device typically includes a processor (ormultiple processors) that executes program instructions or modulesstored in a memory or other non-transitory computer-readable storagemedium or device. The various functions disclosed herein may be embodiedin such program instructions, although some or all of the disclosedfunctions may alternatively be implemented in application-specificcircuitry (e.g., ASICs or FPGAs) of the computer system. Where thecomputer system includes multiple computing devices, these devices may,but need not, be co-located. The results of the disclosed methods andtasks may be persistently stored by transforming physical storagedevices, such as solid state memory chips and/or magnetic disks, into adifferent state.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Detailed Description using thesingular or plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list. The word “exemplary” is usedexclusively herein to mean “serving as an example, instance, orillustration.” Any implementation described herein as “exemplary” is notnecessarily to be construed as preferred or advantageous over otherimplementations.

The disclosure is not intended to be limited to the implementationsshown herein. Various modifications to the implementations described inthis disclosure may be readily apparent to those skilled in the art, andthe generic principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. The teachings of the invention provided herein can beapplied to other methods and systems, and are not limited to the methodsand systems described above, and elements and acts of the variousembodiments described above can be combined to provide furtherembodiments. Accordingly, the novel methods and systems described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the disclosure. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the disclosure.

1. A method for performing reactive evaporation, the method comprising:positioning a volume of refractory material to be evaporated within anevaporation chamber; forming a vacuum environment within the evaporationchamber; providing a beam of electrons to the volume of refractorymaterial to evaporate the refractory material into evaporated particles;and introducing a flow of reactive gas into the evaporation chamber toallow at least some of the reactive gas to react with at least some ofthe evaporated particles of the refractory material, the flow ofreactive gas selected such that a layer formed on a substrate bydeposition of the evaporated particles includes a range of a desirableproperty.
 2. The method of claim 1 wherein the refractory materialincludes tantalum (Ta).
 3. The method of claim 2 wherein the reactivegas includes nitrogen gas (N₂).
 4. The method of claim 3 wherein thelayer includes tantalum nitride (TaN).
 5. The method of claim 4 whereinthe tantalum nitride has a composition expressed as TaN_(x), thequantity x having a value in a range between 0 and 0.5.
 6. The method ofclaim 1 wherein the desirable property includes a mechanical property.7. The method of claim 6 wherein the selected flow of reactive gas is ina range having a lower flow limit and an upper flow limit.
 8. The methodof claim 7 wherein the lower flow limit of the range is selected tocorrespond to be at or higher than a first flow rate that yields a firststress level associated with the layer.
 9. The method of claim 8 whereinthe first stress level includes a stress level associated withtransition between tensile stress and compressive stress associated withthe layer.
 10. The method of claim 9 wherein the first stress level hasa value of approximately zero.
 11. The method of claim 9 wherein thelower flow limit of the range is selected such that the layer provides acompressive stress to the substrate.
 12. The method of claim 11 whereinthe lower limit and the upper limit of the range are selected such thatthe compressive stress has a magnitude less than a selected value. 13.The method of claim 11 wherein the lower limit of the range is selectedsuch that the compressive stress varies sufficiently slowly as afunction of the flow to be substantially reproducible.
 14. The method ofclaim 13 wherein the desirable property further includes an electricalproperty.
 15. The method of claim 14 wherein the electrical propertyincludes a sheet resistance associated with the layer, the sheetresistance increasing as a function of the flow of the reactive gas. 16.The method of claim 15 wherein the upper limit of the range is selectedsuch that the sheet resistance associated with the layer is less than aselected sheet resistance value.
 17. The method of claim 1 furthercomprising forming one or more additional layers over the layer formedwith the flow of reactive gas.
 18. The method of claim 17 wherein eachof the one or more additional layers is formed by electron-beamevaporation, such that all of the layers are formed utilizing onephotolithography and one deposition type.
 19. A reactive evaporationsystem comprising: an evaporation chamber configured to hold a volume ofrefractory material to be evaporated; a vacuum system in communicationwith the evaporation chamber, the vacuum system configured to provide avacuum environment within the evaporation chamber; an electron-beamsystem configured to provide a beam of electrons to the volume ofrefractory material to evaporate the refractory material into evaporatedparticles; and a gas supply system in communication with the evaporationchamber, the gas supply system configured to provide a flow of reactivegas into the evaporation chamber to allow at least some of the reactivegas to react with at least some of the evaporated particles of therefractory material, the flow of reactive gas selected such that a layerformed on a substrate by deposition of the evaporated particles includesa range of a desirable property.
 20. A method for forming a metalizedstack on a semiconductor substrate, the method comprising: mounting thesemiconductor substrate within an evaporation chamber; positioning avolume of refractory material to be evaporated within the evaporationchamber; forming a vacuum environment within the evaporation chamber;and depositing a refractory material barrier layer on the semiconductorsubstrate, the depositing including providing a beam of electrons to thevolume of refractory material to evaporate the refractory material intoevaporated particles, the depositing further including introducing aflow of reactive gas into the evaporation chamber to allow at least someof the reactive gas to react with at least some of the evaporatedparticles of the refractory material, the flow of reactive gas selectedsuch that the refractory material barrier layer includes a range of adesirable property.
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